The head of the Nicaraguan Central Bank, who was considered one of the key civilians in the Sandinista government and was largely responsible for keeping the country's increasingly desperate economy afloat, has resigned and left Nicaragua in an apparent dispute with its political leadership.

The departure of Alfredo Cesar, a young Stanford graduate who successfully renegotiated $900 million in foreign debt inherited by the revolutionary regime when it came to power in July 1979, is the latest in a series of defections that have shaken the leftist government in Managua.

Cesar's resignation is likely to affect the Sandinistas' already troubled relationship with the domestic private sector and may raise questions among foreign bankers whose confidence in Nicaragua has depended to some degree on his personal credibility, according to informed Nicaraguan sources.

A terse official decree issued in Managua Tuesday said only that Cesar's appointment had been rescinded and he had been replaced as Central Bank head by Deputy Planning Minister Luis Enrique Figueroa. Newspapers in the capital, subject to censorship under a government state of emergency, reportedly were instructed to print only the official statement.

The Nicaraguan Embassy in Washington said it had no additional information.

Associates of Cesar and informed sources reached yesterday in Nicaragua and the United States said he left Nicaragua several weeks ago on his honeymoon and later informed the government from outside the country that he did not intend to return.

Located yesterday in Miami, Cesar said through intermediaries that he did not yet want to discuss publicly his resignation or the reasons for it. He is believed to have left the United States last night for another Latin American country.

As the director of Nicaragua's International Reconstruction Fund in 1979 and 1980, Cesar was credited with obtaining substantial amounts of foreign aid and investment capital for the fledgling government, as well as renegotiating the enormous Somoza-era debt, 75 percent of which was held by U.S. banks.

More recently, as Central Bank head, he has been a key figure in attempts to dispel mutual mistrust between the Sandinistas and the Nicaraguan private business community, which has contributed to falling domestic production, unemployment and economic stagnation.

Although they maintain there was no immediate issue that caused the break, sources close to Cesar pointed to what they said was his growing frustration over what he felt was Sandinista politicization of the economy and a misplaced belief that the Soviet Bloc could be counted on to make up shortfalls.

There was no indication yesterday that Cesar intended to join forces with other prominent Nicaraguans who have left the country charging that the Sandinistas have become increasingly authoritarian and protesting their close ties to Cuba and the Soviet Union.

Chief among them is Eden Pastora, the military hero of the 1979 civil war that overthrew the Somoza dictatorship and former deputy interior minister and head of the Sandinista militia. Pastora, who surfaced several weeks ago in San Jose, Costa Rica, has denounced the nine-man Sandinista directorate for betraying the ideals of the revolution and has announced his intention to oust the government.

Almost from the beginning, the Sandinista leaders have denounced counterrevolutionary plots inside and outside the country and used them to justify tighter control. Although this caused concern among some supporters, the claims were given some credibility by the establishment of commando training camps outside the country by Somoza partisans in exile.

Recent months have brought an increase in commando attacks across the border from neighboring Honduras as well as incidents of domestic sabotage.

Pastora has been joined in Costa Rica by a growing number of defecting Nicaraguan military and police officials. He also is known to have been in contact with Alfonso Robelo, a Nicaraguan politician and businessman and a former member of the ruling Sandinista junta who fled the country last month.

Another member of the Sandinistas' original economic team, former Central Bank president Arturo Cruz, who later served in the junta and as ambassador to the United States, resigned from the government late last year and has not returned to Nicaragua. Last fall, Haroldo Montealegre, who replaced Cesar as director of the International Reconstruction Fund, resigned and moved to exile in the United States.